The number of flights in and out of Chicago airports was steadily rising Sunday after a fire at an Aurora radar facility wreaked havoc on the nation’s air-travel system, federal aviation officials said, but the time frame for normal operations remained unclear.

Departing and arriving flights at O’Hare International Airport were around 60 percent capacity Sunday, according to a Federal Aviation Administration statement, and were at 75 percent at Midway Airport.

Hundreds of flights have been canceled at both airports since Friday morning’s fire at one of the nation's busiest air traffic control centers.

The damaged Aurora facility will be fully operational by Oct. 13, according to Sunday’s FAA statement. The statement did not say when O’Hare and Midway would return to normal operations, and a spokesman could not be reached Sunday night.

The FAA brought in technicians from around the country to speed up the repairs. The first shipment of replacement equipment was scheduled to arrive late Sunday night, with more deliveries expected over the next few days.

While teams work around the clock to restore network connections at the facility, air traffic controllers who normally work at the Aurora facility are now working at surrounding air traffic facilities and other high-altitude traffic centers.

As of Sunday evening, airlines had canceled more than 700 flights in and out of O’Hare and nearly 500 flights experienced delays, according to the flight-tracking website FlightAware, which also showed that 56 flights had been canceled Sunday in and out of Midway and that more than 260 were delayed.

All flights in and out of O'Hare International and Midway airports were halted Sept. 26, 2014, after a fire broke out at a radar facility in Aurora.

After the facility was damaged Friday, air traffic controllers have been working from dozens of facilities to safely move air traffic around the Chicago area, according to a press release sent out Sunday by The National Air Traffic Controllers Association.

“This is one of the most challenging situations that air traffic controllers and other FAA employees have faced since 9/11,” the association’s President Paul Rinaldi was quoted as saying in the press release. “The damage to this critical facility is unlike anything we have seen before. Since the first moment when radar scopes went dark at Chicago Center Friday morning, controllers have ensured the highest level of safety at all times.”

Four facilities in Cleveland, Indianapolis, Kansas City and Minneapolis, have taken over the damaged facility’s responsibilities, according to the release. Each has worked with Terminal Radar Approach Control facilities in cities across the Midwest, including Chicago, Milwaukee, Fort Wayne and South Bend.

“You try to affect the smallest number of people,” said Freed, adding that 23 of the larger main line” flights were among the cancellations, he said. “In general, I think people understand that the FAA is doing the best it can, and we’re doing the best we can. It’s a difficult situation.”

United Airlines canceled about 200 flights Sunday, according to a statement issued by spokeswoman Mary Clark.

“Due to continued airspace capacity restrictions, we expect to operate about two thirds of our nearly 600 scheduled departures from Chicago-O’Hare on Sunday,” she said. “We are working with the FAA to minimize the inconvenience to our customers as much as possible.”

Passengers are encouraged to check their airlines’ website or mobile app for the latest information about their flight.

Four other regional radar centers in the Midwest are working overtime to direct air traffic that would normally be tracked through the Aurora center, and are adding dedicated phone lines to communicate among the different regional sites, said Doug Church, a spokesman for the National Air Traffic Controllers Association.

U.S. Sen. Dick Durbin said today that after learning of the extent of damage at the FAA’s radar facility in Aurora, flight delays at Chicago airports are likely to continue into the work week until new computer equipment can be installed.

Durbin, the state’s senior senator, said he spoke this morning with FAA Administrator Michael Huerta, and learned that 23 out of 29 computer racks were destroyed in the Friday morning fire that allegedly was set by contract Harris Corp. employee Brian Howard as part of a suicide attempt. Seven of the computer racks, owned by Harris, are set to be replaced today and the remainder this week, Durbin said.

“They’ve set up some alternative communication lines with other Midwestern cities and they’re going to do the real evaluation this afternoon and let the airlines know how quickly they can restore the flow” of air traffic, Durbin said of the FAA in an interview on WGN (AM-720).

Durbin said Huerta “understands the priority in getting O’Hare and Midway back into service. I hope as late as tonight or early as tomorrow morning they can give the airlines an update as to what the traffic flow is going to be during this week.”

Still, Durbin said, “I think that goes without saying there’s some limitations (on air travel) because of this damage that’s been done.”

Durbin said the FAA is “going to look into it more deeply to see if Harris knew or should have known that there was something unusual here” involving Howard and his background.

To avoid any future issues, Durbin said security failed to inspect the suitcase Howard brought into the facility, which he said held a gasoline container.

“A couple of things come to mind: First inspecting whatever the employees bring in, even if they have security clearance going in and secondly, making sure that in critical positions, like the one where he was posted, there are two people. Not one, but two people. Now I know that’s more expense, but look at the expense associated with this disaster,” he said.

Thousands of travelers worked to reschedule canceled flights on Saturday at Chicago's airports.

Melanie Curtis, of Boise, Idaho, said she had to spend Friday night at an O'Hare motel because her Friday afternoon flight was canceled. Much of that time was spent reserving a Saturday flight to Washington, D.C., she said.

“We were in line after line after line,” Curtis said. “We were on the phone standing in line. One of her co-workers arranged a Saturday afternoon flight, she said.

Curtis, 56, who runs a nonprofit in Boise, said she and her colleagues were taking the delays in stride, especially after meeting other travelers with much worse situations, such as one man who missed his grandfather's funeral.

“We’re fine and we’ll make it,” she said, adding that her group, with the extra time, went and tried Chicago pizza for the first time.

A couple hosting a wedding rehearsal dinner at Spiaggia, a high-end downtown Italian restaurant favored by President Obama, had to round up local friends to fill seats after some out-of-town guests couldn’t make it, said a spokesman for the restaurant, David Semanoff.